The present invention relates generally to bypass turbofan jet engines and more particularly to a bearing support for the fan and compressor of such an engine with the fan at the front (generally called a front-fan engine) which eliminates the need for conventional engine frames.
Front-fan engines derive some of their thrust from a core turbojet engine and some of their thrust from a front fan wherein the outer portion of the airflow from the front fan bypasses the core turbojet engine. Front fans, driven by a section of the core engine's turbine, act like propellers to supply thrust to the engine.
The core turbojet engine includes a compressor followed in order by a combustor, a turbine, and an exhaust nozzle. The compressor compresses incoming air for better combustion of the fuel injected into the combustor. The fuel-air mixture ignites, and the burning gases from the combustor turn the turbine blades to drive the compressor and then exit the exhaust nozzle to supply thrust to the engine. Known front-fan engines generally have two engine frames whose sole purpose is to support the bearings of the front fan and the core turbojet engine's compressor. These engine frames add weight to the engine, and their elimination would result in improved specific fuel consumption and lower manufacturing cost.
The fans and compressors include rotating blades whose tips clear surrounding ducts. The required clearances are determined in part by the radial spring constants of the engine frames. A higher radial spring constant allows a smaller required clearance, thereby decreasing leakage and thus also acting to improve the specific fuel consumption.
It is known, in engines consisting only of a core turbojet engine, to eliminate the engine frame which supports the compressor, and instead the compressor bearing can be supported by a row of compressor guide vanes which act in a dual airflow-guiding and bearing-support role. In other known jet engines, turbine nozzle vanes (or support rods running through the vanes) support a turbine bearing.
However, such expedients have not been available in front-fan engines to support the fan and compressor bearings even though it is desirable to provide such support without the need for heavy engine frames.
In describing the invention, the terminology "structural fan stators" and "structural compressor guide vanes" will be used. For the purpose of this invention, a "structural fan stator" is a fan stator (or portion thereof) which takes a load or is a fan stator enclosing a rod (or the like) which takes a load. Similarly, for the purpose of this invention, a "structural compressor guide vane" is a compressor guide vane (or portion thereof) which takes a load or is a compressor guide vane enclosing a rod (or the like) which takes a load. It is understood that for an engine having a variable stator or guide vane, the pitch controllable portion thereof does not take a load.